In order to clean a solid surface to preserve metal against deterioration, remove graffiti from stone or simply to degrease or remove dirt or other coatings from a solid surface, it has become common practice to use an abrasive blasting technique wherein abrasive particles are propelled by a fluid against the solid surface in order to dislodge the previously applied coatings, scale, dirt, grease or other contaminants. Such abrasive blasting has been used favorably, for example, to degrease metal and is being increasingly used as a replacement for the environmentally hazardous solvent cleaning treatments.
Various abrasive blasting techniques have been used to clean a surface including dry blasting which involves directing the abrasive particles to the surface by means of pressurized air, wet blasting in which the abrasive blast media is directed to the surface by a pressurized stream of water, and a process in which both air and water are utilized either in combination at sufficient pressures to propel the abrasive blast media to the surface as disclosed in U.S. Pat. No. 4,817,342, or in combination in which relatively low pressure water is used primarily as a dust control agent or to control substrate damage.
The blast media or abrasive particles most widely used for blasting surfaces either by dry or wet blasting to remove adherent material therefrom is sand. Sand is a hard abrasive which is very useful in removing adherent materials such as paint, scale and other materials from metal surfaces such as steel. While sand is a most useful abrasive for each type of blasting technique, there are disadvantages in using sand as a blast media. For one, sand, i.e., crystalline silica, is friable and upon hitting a metal surface will break into minute particles which are small enough to enter the lungs. These minute silica particles pose a substantial health hazard. Additionally, much effort is needed to remove the sand from the surrounding area after completion of blasting. Still another disadvantage is the hardness of sand itself. Thus, sand cannot be readily used as an abrasive to remove coatings from relatively soft metals such as aluminum, or non-metallic substrates such as plastic, plastic composite structures, concrete or wood, as such relatively soft substrates can be excessively damaged by the abrasiveness of sand. Moreover, sand cannot be used around moving parts of machinery inasmuch as the sand particles can enter bearing surfaces and the like.
An alternative to sand as a blast media, particularly, for removing adherent coatings from relatively soft substrates such as softer metals as aluminum, or plastic composite surfaces and the like is sodium bicarbonate. While sodium bicarbonate is softer than sand, it is sufficiently hard to remove coatings from any metal surface and as well remove coatings including paint, dirt, and grease from non-metallic surfaces without harming the substrate surface. Sodium bicarbonate is not harmful to the environment and is most advantageously water soluble such that the particles which remain subsequent to blasting can be simply washed away without yielding environmental harm. Since sodium bicarbonate is water soluble and is benign to the environment, this particular blast media has found increasing use in removing coatings and cleaning dirt, grease and oil and the like from metal and a variety of other surfaces.
Sodium bicarbonate is also a friable abrasive and, like sand, will form a considerable amount of dust during the blast cleaning process. To control the dust formed by the sodium bicarbonate blast media as it contacts the targeted surface, water has been used as the pressurized fluid stream to carry the sodium bicarbonate particles to the target surface or included in the compressed air carrier medium either internally in the nozzle or directed as an external stream onto or surrounding the stream of the abrasive particles for dust control. Each of these processes is considered wet blasting.
Various techniques are known for introducing a particulate abrasive into a water stream, for example, by introduction of a separate air stream which carries the particulate abrasive into the throat of a venturi-type blast nozzle through which the water carrier is passing, or by mixing the particulate abrasive/air stream exterior of a blast nozzle means with the liquid-stream as disclosed in U.S. Pat. No. 4,125,969. For convenience of operation, the particulate abrasive and water have conventionally been allowed to mix while traveling through the interior of the blast nozzle which is used to direct the abrasive/water mixture to the work surface at high velocity.
While water soluble abrasive media such as sodium bicarbonate is finding increasing use in the cleaning industry as a blast media for cleaning metals such as steel and, in particular, softer metals such as aluminum, copper, brass, etc. and softer non-metallic substrates such as plastic, plastic composites, wood, concrete, etc., due to the fact that the sodium bicarbonate blast media is safe to use, safe for the environment, and provides a relatively easy clean-up from the work site, upon wet blasting and subsequent drying of the target surface, there can remain a film of the sodium bicarbonate media which remains on the surface of the substrate. Even after rinsing the substrate with water, this residue can remain leaving an unsightly film on the clean surface or provide the surface with a dull finish. In U.S. Pat. Nos. 5,308,403 and 5,316,587, both of which are herein incorporated by reference, and assigned to Church & Dwight Co., a rinse aid is mixed with the sodium bicarbonate blast media to effect removal of this residual film during wet blasting and rinsing. The rinse aid can be a surfactant, magnesium oxide or a combination thereof. The addition of the rinse aid has been very effective for greatly reducing if not eliminating the residue of sodium bicarbonate blast media which remains on a clean surface, especially flat surfaces subsequent to wet blast cleaning.
The amount of surfactant used to provide reduced residue content and easily rinsed residues is extremely small in most cases and, thus, typically ranges from about finite levels to about 3 wt. %, preferably about 0.05 to about 1 wt. %, and, more preferably, from about 0.05 to 0.5 wt. % of the abrasive blast media particles. Moreover, the addition of the surfactant actually aids in removing any dirt, grease or oil from the substrate. Nonionic surfactants appear to best provide the additional detersive action. Surfactant levels provided to aid in removing any dirt, grease or oil from the substrate can be much higher and, thus, range from about 0.1 to 30 wt. % relative to the blast media. Thus, it is useful to provide several kinds of surfactants with the blast media including those most readily able to reduce residue formation such as anionic surfactants and those capable of enhancing the removal of dirt, grease or oil from the substrate. The surfactant advantageously solubilizes the dirt and grease allowing easier clean up and reduces the deflection of dirt from one surface to another.
The addition of surfactant to water soluble abrasive blast media such as sodium bicarbonate has been very helpful in removing residual films of the abrasive during wet blasting and to enhance the cleaning effect of the abrasive media. Unfortunately, during wet blasting, even minute amounts of the surfactant can cause excessive foaming in the effluent. The presence of foam can make the effluent more difficult to contain and dispose of. Further, it has recently been suggested to use a slurry blasting process in which sodium bicarbonate abrasives are dispersed in a relatively low pressure water stream and directed against the targeted surface which is situated in a blast cabinet. The used slurry can be recycled and again directed at the substrate surface. Excessive foaming in the blast cabinet causes overflow of slurry which is to be recycled and decreases pumping efficiency during the recycling process.
Accordingly, it would be useful to incorporate a surfactant into an abrasive blast media whether to aid in the rinsing of residual films of the abrasive left on the substrate surface after cleaning or to aid in the removal of the contaminants from the surface and be able to reduce the amount of foam which is produced during wet blasting of such blast media.
It is, therefore, a primary objective of the present invention to reduce the amount of foam produced during the wet blasting of an abrasive media which further contains a surfactant.
Another objective of the present invention is to provide a blast media which comprises abrasive particles, a surfactant and an agent which reduces the amount of foam produced during the wet blasting of the media on a target surface for the removal of contaminants therefrom.
These and other objects of the invention will become readily apparent upon a review of the description of the invention below and the appended claims.